Ignition and control system for gas burners

ABSTRACT

A ceramic glow igniter is connected in series with the hot-wire actuating element of a normally open thermal relay across a power source through a double-throw switch when in its cold position. This causes heating of the igniter to ignition temperatures, causes the hot wire element to expand and close the relay, and the heat of the igniter causes the double-throw switch to move to its hot position thus breaking the igniter and hot wire circuit. The electromagnetic winding of a normally closed solenoid gas valve is connected across the power source through the now-closed relay and the double-throw switch, now in its hot position, causing the gas valve to open. Due to thermal lag, the gas valve opens before the thermal relay opens and ignition of the gas occurs before the igniter cools. Burner flame maintains the double-throw switch in its hot position, and a current limiting resistor connected across the relay holds the solenoid gas valve open.

United States Patent 1 Wright IGNITION AND CONTROL SYSTEM FOR GAS BURNERS [75] Inventor: James A. Wright, Webster Groves,

[73] Assignee: Emerson Electric Co., St Louis, Mo.

[22] Filed: May 10, 1972 [21] Appl. No.: 252,122

[ Dec. 4, 1973 [5 7 ABSTRACT A ceramic glow igniter is connected in series with the hot-wire actuating element of a normally open thermal relay across a power source through a double-throw switch when in its cold position. This causes heating of the igniter to ignition temperatures, causes the hot wire element to expand and close the relay, and the heat of the igniter causes the double-throw switch to move to its hot position thus breaking the igniter and hot wire circuit. The electromagnetic winding of a normally closed'solenoid gas valve is connected across the power source through the now-closed relay and the double-throw switch, now in its hot position, causing the gas valve to open. Due to thermal lag, the gas valve opens before the thermal relay opens and ignition of the gas occurs before the igniter cools. Burner flame maintains the double-throw switch in its hot position, and a current limiting resistor connected across the relay holds the solenoid gas valve open.

7 Claims, 1 Drawing Figure AAAAAAAA IGNITION AND CONTROL SYSTEM FOR GAS BURNERS This invention relates to ignition and control systems for the safe and automatic operation of gas burners, particularly to those systems employing glow igniters and normally closed, electromagnetically operated, fuel control valves and to an arrangement wherein the igniter is operated only for a sufficient period to ignite the gas.

In my co-pending application, Ser. No. l 1 1,425, filed Feb. 1, 1971, l disclose a gas burner ignition and control system employing a ceramic glow igniter. In this arrangement, a resistance heater series connected with the glow igniter causes a normally open thermal relay to close and effect the energization and opening of a normally closed, solenoid operated, fuel control valve only after sufficient current flows through'the series connected igniter for a sufficient period of time to insure that the igniter has attained ignition temperature. Continued energization of the resistance heater and igniter is required in this arrangement during burner operation to maintain the fuel valve open.

An object of this invention is to provide a generally new and improved ignition and control system for gas burners employing a ceramic glow igniter in which the igniter is energized upon starting only for a sufficient period of time to effect opening of the solenid gas valve by its radiant energy at ignition temperature.

A further object is to provide a system of this kind in which current flow through the igniter and the radiant energy of the igniter at ignition temperature effects the closure of switching means at two separate points in a circuit to complete an energizing circuit to open a normally closed solenoid operated valve.

A further object is to provide a system of this kind in which temperature responsive switching means responds to the radiant energy of the glow igniter to effect a flow of fuel to the burner and to simultaneously de-energize the igniter and then responds to flame at the burner to maintain the flow of fuel thereto, the mass of the igniter being such as to retain an ignition temperature for a sufficient period after deenergization thereof to ignite the fuel.

A further object is to provide a system of this kind in which a first switching means responsive to the radiant energy of the glow igniter and a second switching means responsive to current flow through the igniter at ignition temperature jointly complete a circuit to effect the pull-open engergization of a biased closed, solenoid operated valve. When the igniter attains ignition temperature, the first switching means simultaneously deenergizes the igniter and responds to the radiant energy of the flame at the burner to complete a hold-open but not a pull-open energizing curcuit for the solenoid operated valve.

Further objects and advantages will appear from the following description when read in connection with the accompanying drawing.

The single FIGURE of the drawing is a schematic illustration of an ignition and control system for gas burners constructed in accordance with the present invention.

Referring to the drawing, the primary elements of the system are: a gas burner 10, a normally closed, solenoid operated, fuel control valve 12 including a solenoid winding 14 and interposed in a gas supply conduit 13 leading from a source of supply to the burner 10, a eeramic glow igniter 16, a double-throw, temperature responsive switch 18, a hot-wire actuated switch 20, a current limiting resistor 22, a fuse 24, a space thermostat 26, and power source terminals 28 and 30.

The double-throw switch 18 has a bowed bimetal blade 32, shown in its normal cold position in which it engages contact 34. The bimetal blade 32 is arranged to respond to the radiant energy of the glow igniter 16 or to the radiant energy of flame at burner 10 to snap through a planar shape to an oppositely bowed hot position, as shown in dotted line, in engagement with a contact 36.

The switch 20 comprises a stationary contact 38 mounted on a conductive bracket 39 and a movable contact 40 mounted on a conductive flexible blade or arm 42. The blade 42 is formed so as to normally bias movable contact 40 into engagement with contact 38. However, the contact 40 is held apart from contact 38 in a switch-open position by a conductive hot wire element 44, attached at one end to the blade 42 and at its other end to a'conductive bracket 46, when the wire element 44 is at normal ambient temperature. When sufficient current is passed through hot wire element 44, it is heated and elongates rapidly permitting contact 40 to close with contact 38, and when such current flow is cut off, it contracts to open contacts 38 40. The relatively small mass of hot wire element 44 and the relatively high temperature with respect to usual ambient temperatures to which it is heated rapidly by current flowing therethrough results in a relatively rapid response in both directions.

The ceramic glow igniter 16 is preferably a commercially available igniter constructed of silicon carbide, with sufficient mass for the purpose to be described and sufficient electrical resistance at gas ignition temperatures to preclude runaway current flow therethrough.

The glow igniter 16 is connected across power source terminals 28 and 30 in series with the space thermostat 26, the double-throw switch in its cold position as shown, and the hot wire element 44. Current can therefore flow through the hot wire element 44 only when it flows through igniter-16. The winding 14 of solenoid valve 12 is connected across power source 28 and 30 in series with the space thermostat 26, the doublethrow switch 18 when in its hot, dotted line position, the fuse 24, and contacts 38-40 of switch 20 when they are closed. These connections provide sufficient energization of winding 14 to effect the opening of fuel control valve 12 against its closing bias.

The resistor 22 is connected across the contacts 38-40 of switch 20 and provides limited energization of winding 14 to hold solenoid valve 12 open when contacts 3840 open. The resistor 22 is of such value as to permit sufficient energization of winding 14 at the available power source voltage to hold the valve 12 open, but prevents sufficient energization thereof to pull the valve open from its closed position.

OPERATION The system is shown in the cold position it assumes when thermostat 26 has been open for some time. When space thermostat 26 closes in response to a drop in temperature of the space being heated by burner 10, the series connected glow igniter l6 and hot wire actuator 44 are energized and heated by current passing therethrough. The resistance and mass of wire actuator 44 are such that is is heated sufficiently to elongate and permit contacts 38-40 to close somewhat before the greater mass of the glow igniter 16 is heated to ignition temperature.

When the temperature of igniter 16 attains and preferably slightly exceeds the ignition temperature of the gaseous fuel, sufficient energy is radiated therefrom to heat bimetal switch blade 32 of switch 18 and cause it to snap from its solid line position to its dotted line position, thereby closing with contact 36 and breaking with contact 34. When this occurs, the solenoid widning 14 is energized through switches 18 and 20 sufficiently to pull open fuel control valve 12, and the igniter l6 and wire actuator 44 are substantially simultaneously de-energized. The time required to open valve 12 is considerably less than the time required for wire actuator 44 to cool and shorten sufficiently to open contacts 38-40 of switch 20, even though the response time of switch 20 is relatively short compared to bimetal actuated switches. Once valve 12 has been opened, the winding 14 is energized sufficiently through the switch bypassing resistor 22 to hold the valve open when switch contacts 38-40 open.

When fuel valve 12 is opened, fuel immediately emerges from burner and is ignited by igniter 16. The ceramic igniter 16, due to its mass, retains a sufficiently high temperature for a sufficient period of time after being de-energized to ignite the fuel at burner 10 and to retain switch blade 32 in its dotted line position. When the fuel is ignited, the blade 32 is heated by the burner flame and maintained in its dotted line position so long as burner flame persists. The burner now continues to operate normally until thermostat 26 opens, thereby breaking the hold-open circuit for winding 14.

The opening of switch contacts 38-40 shortly after switch blade 32 moves to its hot, dotted line position prevents the pull-open energization of solenoid winding 14 and the opening of valve 12 immediately following a momentary circuit interruption or power failure which permits the valve to close and resulting extinguishing of burner flame. When the hold-open circuit for solenoid winding 14 is interrupted for any reason, due to power failure or the opening of some additional control switch therein (not shown), during normal operation of the burner, permitting the valve to close,

it will not reopen immediately upon restoration of power or reclosing of such control switch. Under these conditions, the valve will remain closed until switch blade 32 cools and snaps back to its solid line position to complete the circuit for igniter 16 and actuator wire 44, causing contacts 38-40 to close, and thereafter until switch blade 32 again snaps over to its dotted line position due to radiant energy of the igniter.

It will be understood that the time required for bimetal blade 32 to cool and move to its solid line position to re-energize the igniter, plus the time required for the igniter to reach ignition temperature, is such that considerable unburned gas would escape from the burner if the fuel valve were opened immediately following a circuit interruption during normal operation of the burner.

If, for any reason, the fuel fails to ignite upon starting or if the burner flame is extinguished during normal operation, the switch blade 32 will cool and snap over to its solid line position, thereby breaking the valve hold-open circuit. The valve 12 will then close and remain closed until the igniter reaches ignition temperature and until the blade 32 is again heated thereby sufficiently to snap over to its dotted line position. Thus, a scavenging period is provided in which to disperse any unburned fuel escaping from the burner between the time the flame is extinguished and the time blade 32 has cooled sufficiently to break with contact 36.

The fuse 24 is calibrated to break to valve pull-in circuit extending through switch contacts 38-40 in a short period of time in event actuator wire 44 breaks or burns out permitting contacts 38-40 to remain closed.

Modifications of the foregoing arrangement which fall within the spirit of the invention will occur to those skilled in the art. For example, a warping bimetal blade through which the igniter current is passed may be substituted for the elongating and contracting wire actuator element 44. Also, such bimetal blade may be heated indirectly to effect its warping by the provision of an adjacent resistance heater through which the igniter current is passed. It is only necessary to the operation of the system that the means actuating the switch 20 is responsive to current flow through the igniter, that the switch contacts 38-40 are closed before blade 32 is heated sufficiently to close with its hot side contact 36, and that such actuator has sufficient lag (in the order of one or two seconds) to hold contacts 38-40 closed until the valve 12 is opened.

I claim:

1. In a burner control system, a burner, a biased closed solenoid fuel supply valve including a winding, an electrical power source, a glow igniter, circuit connections including a double-throw, snap-acting, temperature responsive switch in its cold position connecting said igniter across said power source, circuit connections including said double-throw switch in its hot position and a normally open switch when closed connecting said winding across said power source to effect opening of said valve, switch actuating means connected in series with said igniter and operative in response to current flow through said igniter to close said normally open switch, said double-throw switch being responsive to radiant energy of the igniter at gas ignition temperature to snap from its cold to hot position, thereby to de-energize said igniter and switch actuating means and to energize said valve winding substantially simultaneously, said igniter having sufficient mass to retain a gas ignition temperature long enough after deenergization to ignite fuel at said burner, said switch actuating means being responsive to current flow through said igniter to close said biased open switch before said igniter reaches gas ignition temperature and having sufficient lag after de-energization to retain said switch closed until said fuel valve is opened, said double-throw switch being further responsive to flame at said burner to remain in its hot position, and circuit means including said double-throw switch in its hot position connecting said winding across said power source for a limited energization thereof sufficient to hold said valve open but insufficient to pull the valve open from its biased closed position.

2. The burner control system claimed in claim 1 in which said glow igniter is constructed of silicon carbide and has sufficient mass to retain an ignition temperature for a sufficient period after de-energization to ignite fuel flowing from the burner.

3. Theburner control system claimed in claim 2 in which said double-throw switch responds to an igniter temperature slightly above gas ignition temperature to snap from its cold to hot position.

4. In a burner control system, a burner, and electrical power source, a ceramic glow igniter, a biased closed solenoid gas valve including a winding, a temperature responsive double-throw switch having a cold position in which it completes a circuit connecting said igniter across said power source and having a hot position to which it moves in response to the radiant heat of said igniter at gas ignition temperature thereby deenergizing said igniter, a normally open switch, switch actuating means including means connected in series with said igniter and operative in response to current flow through said igniter to close said normally open switch before said igniter reaches ignition temperature, circuit connections completed through said doublethrow switch when in its hot position and through said normally open switch when closed connecting said valve winding across said power source to effect opening of said gas valve, said igniter having sufficient mass to retain an ignition temperature long enough after deenergization to ignite fuel flowing from said burner, and said double-throw switch being further responsive to burner flame to remain in its hot position, circuit connections including impedance means completed through said double-throw switch in its hot position connecting sad vlave said valve winding across said power source for limited hold-open energization thereof, and said switch actuating means having sufficient response lag following de-energization of said igniter to permit opening of said valve.

5. The burner control system claimed in claim 4 in which said normally open switch is biased closed switch normally open by a conductive wire element and in which said wire element is heated by current flow and elongates sufficiently to permit said switch to close.

6. The burner control system claimed in claim 4 in which said valve opening circuit further includes therein means responsive to the current flow therethrough for a predetermined short period of time to break said circuit.

7. The burner control system claimed in claim 6 in which said current flow responsive means is a fusible link. 

1. In a burner control system, a burner, a biased closed solenoid fuel supply valve including a winding, an electrical power source, a glow igniter, circuit connections including a double-throw, snap-acting, temperature responsive switch in its cold position connecting said igniter across said power source, circuit connections including said double-throw switch in its hot position and a normally open switch when closed connecting said winding across said power source to effect opening of said valve, switch actuating means connected in series with said igniter and operative in response to current flow through said igniter to close said normally open switch, said double-throw switch being responsive to radiant energy of the igniter at gas ignition temperature to snap from its cold to hot position, thereby to deenergize said igniter and switch actuating means and to energize said valve winding substantially simultaneously, said igniter having sufficient mass to retain a gas ignition temperature long enough after de-energization to ignite fuel at said burner, said switch actuating means being responsive to current flow through said igniter to close said biased open switch before said igniter reaches gas ignition temperature and having sufficient lag after de-energization to retain said switch closed until said fuel valve is opened, said double-throw switch being further responsive to flame at said burner to remain in its hot position, and circuit means including said double-throw switch in its hot position connecting said winding across said power source for a limited energization thereof sufficient to hold said valve open but insufficient to pull the valve open from its biased closed position.
 2. The burner control system claimed in claim 1 in which said glow igniter is constructed of silicon carbide and has sufficient mass to retain an ignition temperature for a sufficient period after de-energization to ignite fuel flowing from the burner.
 3. The burner control system claimed in claim 2 in which said double-throw switch responds to an igniter temperature slightly above gas ignition temperature to snap from its cold to hot position.
 4. In a burner control system, a burner, and electrical power source, a ceramic glow igniter, a biased closed solenoid gas valve including a winding, a temperature responsive double-throw switch having a cold position in which it completes a circuit connecting said igniter across said power source and having a hot position to which it moves in response to the radiant heat of said igniter at gas ignition temperature thereby de-energizing said igniter, a normally open switch, switch actuating means including means connected in series with said igniter and operative in response to current flow through said igniter to close said normally open switch before said igniter reaches ignition temperature, circuit connections completed through said double-throw switch when in its hot posiTion and through said normally open switch when closed connecting said valve winding across said power source to effect opening of said gas valve, said igniter having sufficient mass to retain an ignition temperature long enough after de-energization to ignite fuel flowing from said burner, and said double-throw switch being further responsive to burner flame to remain in its hot position, circuit connections including impedance means completed through said double-throw switch in its hot position connecting sad vlave said valve winding across said power source for limited hold-open energization thereof, and said switch actuating means having sufficient response lag following de-energization of said igniter to permit opening of said valve.
 5. The burner control system claimed in claim 4 in which said normally open switch is biased closed switch normally open by a conductive wire element and in which said wire element is heated by current flow and elongates sufficiently to permit said switch to close.
 6. The burner control system claimed in claim 4 in which said valve opening circuit further includes therein means responsive to the current flow therethrough for a predetermined short period of time to break said circuit.
 7. The burner control system claimed in claim 6 in which said current flow responsive means is a fusible link. 